The bacterial Cu,Zn super oxide dismutases have a limited homology with the well-studied eukaryotic SOD enzymes, yet carry out the same chemical reaction. The seven critical active site histidines are maintained, as well as the metal ions, and are presumably in the same orientation as in the already known structures. The essential bacterial SOD's, with sequences so different from mammalian ones, are likely targets for therapeutic agents for many bacterial diseases. The enzymes for this project are from the human pathogen Neisseria meningitidis and the porcine pathogen Actinobacillus pleuropneumonia, and are overexpressed and purified from E. coli.